1. Field of the Invention
This invention relates to an outboard motor control system, particularly to an outboard motor control system for controlling the operation of a plurality of outboard motors mounted on a boat (hull).
2. Description of the Related Art
When two or more outboard motors are mounted on the stern of a boat (hull) in what is known as a multiple outboard motor installation, the outboard motors are usually connected by a link called tie bar for enabling mechanically interconnected steering of the outboard motors, as taught in Laid-Open Patent Application No. Hei 8(1996)-276896, for example.
In the case of multiple outboard motor installation, boat driving stability can be improved by making extensions of the outboard motors' propeller axes of rotation intersect at a predetermined distance (e.g., about 20 meters) rearward of the mounting location of the outboard motors. (In the following, the point of intersection of the extensions of the outboard motors' propeller axes of rotation will sometimes be called the “stream confluence point.”) In the prior art, therefore, the practice has been to adjust the length and the like of the tie bar interconnecting the outboard motors so as to align the outboard motors at predetermined angles relative to one another.
In addition, a so-called auto-spanker has been developed for individually regulating thrust of the outboard motors of a multiple motor installation so as to automatically maintain the bow direction and position of the boat constant. This is accomplished by detecting the speed and direction of the wind hitting the boat and regulating the shift (gear) position and throttle opening of the outboard motors based on the detected values in order to adjust the direction and magnitude of outboard motor thrust for maintaining the bow direction constant (usually windward) and the keeping the boat stationary.
When multiple outboard motors are mechanically connected by the tie bar as in the prior art, the angles between the outboard motors change with steering of the outboard motors. Because of this, as shown in FIG. 8, the stream confluence point can be made to fall at or approximately at the desired point only when the steering angles of the outboard motors fall within a certain range. Room for improvement in boat driving stability therefore remains.
In addition, it is known that boat turning performance can be regulated by adjusting the stream confluence point. Adjustment of the stream confluence point is therefore effective for regulating the bow direction and position of a boat using an auto-spanker. However, when the angle between the outboard motors is rigidly fixed by the tie bar in the conventional manner, the stream confluence point cannot be freely changed, so that the perfonnanee of the prior art auto-spanker is not satisfactory.